Ischemia means a reduction in blood flow to organs, tissues or a region thereof, caused by contraction or occlusion of blood vessel. Once ischemia occurs, even if reperfusion, it is followed by various sequelas are developed due to the damage of nerve cells. Such ischemia is frequently occurs in coronary artery diseases, cardiovascular diseases, angina pectoris, headache or other symptoms related to blood vessel, and leads to irreversible damage, i.e., necrosis of cells or tissues, at last.
Since the ischemic diseases such as myocardial infarction, arrhythmia or heart failure caused by the cell damage and dysfunction during ischemia-reperfusion have a high morbidity rate, a high mortality rate, and a low complete cure rate, basic researches and clinic studies have been intensively undergone on this field last fifty years [Wang, Q. D. et al., Cardiovasc. Res. 55:25-37, 2002]. Especially, since ischemia-reperfusion injury is involved in various physiological mechanisms including the change of metabolism, immune response and ion homeostasis, generation of oxygen free radicals and the like, studies have actively undergoing on various fields related to immune modulators, cell death suppressors, ion channel modulators, etc. [Hearse, D. J. et al., Mol. Cell. Biochem. 186:177-184, 1998]. Based on such mechanismic researches, there have been developed a number of therapeutics and surgical operations focused on novel acting site so far, but the technique for protecting cardiomyocytes from ischemia-reperfusion injury has not yet been commercialized. Therefore, there is a need for an agent for preventing and treating ischemic heart diseases or a heart protecting agent, which can delay the progress of ischemic damage of cardiomyocytes and reduce reperfusion-induced injuries.
In addition, it has become obvious that if ischemia is disappeared by recovery of blood flow, the generation of reactive oxygen species (ROS) is accelerated, which causes a remarkable decrease of glutathione and brings about more serious diseases. Similar diseases are observed when blood flow stops or recovers during the transplant surgery of various kinds of organs such as heart, liver, lung, pancreas or blood vessel, and will be a problem in incising and removing an organ as well. A reactive oxygen and reactive free radicals assumed to cause diseases, are detected in the cytoplasm and organelle of cells consisting of tissues, especially in mitochondria producing ATP as a main energy source of a cell. In mitochondria, it is observed that the above reactive molecules are mainly released through a respiratory chain, and their concentration is significantly increased during ischemia-reperfusion.
In this regard, since ischemia leads to cell death or necrosis of cells, and especially cell death occurring after reperfusion is a main cause for tissue damage, ischemic cell death is a cause for various ischemic diseases comprising brain ischemia, heart ischemia, diabetic cardiovascular disease, heart failure, myocardial hypertrophy, retinal ischemia, ischemic colitis and ischemic acute renal failure.
In brain ischemia, the depletion of an energy source due to the reduction of blood supply induces ischemic cell death. Then, the ischemic cell death activates a receptor of cell membrane excessively, which is followed by various biochemical alterations including accumulation of glutamic acid and calcium respectively outside and inside of cells, and damage of lipid, protein and nucleic acid, and finally leads to brain tissue injury (Liu, P. K., J. Biomed. Sci. 10:4-13, 2003; Lipton, P., Physiol. Rev. 79:1431-1568, 1999; and Renolleau, S. et al., Stroke 29:1454-1460, 1998).
In case of myocardial infarction, heart failure and arrhythmia as ischemic heart diseases, it has been reported that ischemic cell death occurs by activation of lipid enzyme triggering damages of cell membranes, the changes of pH and calcium transport [Ferrari, R. Rev. Port. Cardiol. 5:7-20, 2000; Webster, K. A. et al., J. Clin. Invest. 104:239-252, 1999; Katz, A. M. et al., J. Mol Cell. Cardiol. 2:11-20, 1985; and Vandeplassche, G. et al., Basic Res. Cardiol. 85:384-391, 1990]. In retinal ischemia, it has been known that cell death of retinal cells mediated by glutamate is concerned with ischemic cell death [Napper, G. A. et al., Vis. Neurosci. 16:149-158, 1999]. Insufficient blood supply to colon causes ischemic cell death, and then, occlusive injury of arteries due to cell necrosis and hemodynamic disorders lead to ischemic colitis as an ischemic disease [Saegesser, F. et al., Pathobiol. Annu. 9:303-337, 1979].
Meanwhile, Minocycline, which is one of the tetracycline antibiotics inhibiting ischemic cell death, has been known to be effective in ischemic diseases such as cerebral infarction [Yrjanheikki, J. et al., Proc. Natl. Acad. Sci. USA 96:13496-13500, 1999], myocardial infarction [Scarabelli, T. M. et al., J. Am. Coll. Cardiol. 43:865-874, 2004] and an ischemic acute renal failure [Wang, J. et al., J. Biol. Chem. 279:19948-19954, 2004], from which it can be known that ischemic cell death is a cause of the above diseases.
Further, it has been known that damage or cell death of nerve cells, induced by ischemia is a main cause of various nervous diseases such as stroke, head trauma, Alzheimer's disease, Parkinson's disease, neonatal hypoxia, glaucoma or diabetic neuropathy [G. J. Zoppo et al., Drugs 54, 9 (1997); I. Sziraki et al., Neurosci. 85, 1101 (1998)].
Based on the intensive research on the development of compounds having pharmacological effect on the above ischemic diseases, the present inventors completed this invention by confirming that novel aminopyrazole derivatives inhibit ischemic cell death, and thus, can be used as an agent for preventing and treating ischemic diseases such as brain ischemia, heart ischemia, diabetic cardiovascular disease, heart failure, myocardial hypertrophy, retinal ischemia, ischemic colitis, ischemic acute renal failure, stroke, head trauma, Alzheimer's disease, Parkinson's disease, neonatal hypoxia, glaucoma and diabetic neuropathy, which are mediated by ischemic cell death, and an agent for protecting organs.